Transmission of data from one device to another can be done using a variety of transmission mediums; including, but not limited to, infrared, coaxial cable, twisted pair, and radio frequency (RF). Each of these transmission mediums has certain advantages and disadvantages. For example, coaxial cable and twisted pair transmission mediums provide highly reliable and private long transmission paths (i.e., low error rate), but require the devices exchanging the data to be physically coupled together. RF and infrared transmission mediums remove the need for physical coupling, but are not private, don't have the transmission range of wireline, and require recovery circuits to have a wide dynamic range.
Because of the convenience of wireless connections (i.e., RF and infrared) many conventional wireline connections (coaxial cable and twisted pair) are being replaced with wireless connections. For example, coupling of a printer to a personal computer has traditionally been accomplished using a coaxial cable, but, because of new developments in infrared technology, such coupling is now being done using an infrared transmission path. One relatively new infrared technology making wireless connection practical is Pulse Position Modulation (PPM). In essence, PPM works by dividing 500 nSec time slots into four sections and providing a light pulse in one of the sections. If the light pulse occurs in the first section, the data being transmitted is representative of digital data 00; in the second section: digital data 01, in the third section: digital data 10; and in the forth section: digital data 11. Thus, PPM provides up to 4 Mbps of data transfer capability, which is more than adequate to support many traditional wireline connections.
While PPM provides sufficient data transmission rates, it requires data recovery circuits to have a wide dynamic range and to be of high fidelity. One such data recovery circuit is a limiting circuit. The limiting circuit includes an amplifier having its gain limited such that when the input signal exceeds a certain threshold, the output of the amplifier is limited to a certain value. The limiting circuit works well (i.e., is of high fidelity) when the magnitude of the received pulse is small but, when the magnitude is large, the output of the amplifier, because of the limiting, distorts the pulse width of the received pulse. Thus, for many applications, the limiting circuit is not acceptable.
Another type of data recovery circuit is a multi-stage automatic gain control (AGC) circuit. The AGC circuit includes at least two AGC stages, an AC coupling element, and an amplifier. While the AGC circuit provides the needed dynamic range and improves the fidelity, in comparison with the limiting circuit, it adds a number of additional components which increases noise. Depending on the noise requirements of a new data recovery circuit design, the AGC may not provide sufficient performance. In addition, because of the additional components, the AGC increases the cost and power of a circuit employing it as well as taking up more real estate. Two critical factors to minimize in the design of integrated circuits (IC).
Therefore, a need exists for a circuit that provides the needed fidelity and dynamic range to recover digital data without the drawbacks of the limiting circuit and the AGC circuit.